Some good links there from GT. I also second CharlieH's comment that as long as you are respectful in contacting an sp, it's hard to go too far wrong.
That said, read the ad's thoroughly and make sure the questions you are asking have not already been answered there. Check their website if they have one as well. Be polite , but get to the point. They are busy and aren't paid to "chat". Avoid being too specific in requests for menu items as that tends to make people uncomfortable. Remember, you are paying for time, nothing else.
And lastly, make sure that the ad you are responding to is real. On sites like LL, it seems like about 2/3 of the ads are fakes sometimes. These bogus ads range from bait and switch to downright money scams. There are lots of legit girls wo advertise there as well, but always make sure you can verify that they are real from other sources such as this site. (If they have multiple recco's from long time gents here, then they are most likely real.) Never send a deposit to anyone that you can't verify as real through another source. That is the number one scam you will see out there. Some legit girls do charge deposits as well, but just make sure you verify they are real first. Think with your northern head, not your southern one π
Checking out the recco page here is a great place to start, as it is easy to verify they are real, and you can judge things from other's experience. You can also send info requests to those who wrote the recco's. Not all gents will respond, but most in my experience are quite helpful when asked.
Good luck and have fun!